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Researchers Submit Patent Application, "Spectral Shift Control for Dimmable Ac Led Lighting", for Approval

May 14, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Grajcar, Zdenko (Crystal, MN); Klassen, Brad (Monticello, MN); Erickson, Leif (Saint Paul, MN), filed on December 30, 2013, was made available online on May 1, 2014.

No assignee for this patent application has been made.

News editors obtained the following quote from the background information supplied by the inventors: "Power factor is important to utilities who deliver electrical power to customers. For two loads that require the same level of real power, the load with the better power factor actually demands less current from the utility. A load with a 1.0 power factor requires the minimum amount of current from the utility. Utilities may offer a reduced rate to customers with high power factor loads.

"A poor power factor may be due to a phase difference between voltage and current. Power factor can also be degraded by distortion and harmonic content of the current. In some cases, distorted current waveforms tend to increase the harmonic energy content, and reduce the energy at the fundamental frequency. For a sinusoidal voltage waveform, only the energy at the fundamental frequency may transfer real power to a load. Distorted current waveforms can result from non-linear loads such as rectifier loads. Rectifier loads may include, for example, diodes such as LEDs, for example.

"LEDs are widely used device capable of illumination when supplied with current. For example, a single red LED may provide a visible indication of operating state (e.g., on or off) to an equipment operator. As another example, LEDs can be used to display information in some electronics-based devices, such as handheld calculators. LEDs have also been used, for example, in lighting systems, data communications and motor controls.

"Typically, an LED is formed as a semiconductor diode having an anode and a cathode. In theory, an ideal diode will only conduct current in one direction. When sufficient forward bias voltage is applied between the anode and cathode, conventional current flows through the diode. Forward current flow through an LED may cause photons to recombine with holes to release energy in the form of light.

"The emitted light from some LEDs is in the visible wavelength spectrum. By proper selection of semiconductor materials, individual LEDs can be constructed to emit certain colors (e.g., wavelength), such as red, blue, or green, for example.

"In general, an LED may be created on a conventional semiconductor die. An individual LED may be integrated with other circuitry on the same die, or packaged as a discrete single component. Typically, the package that contains the LED semiconductor element will include a transparent window to permit the light to escape from the package.

"The applicant's U.S. Ser. Nos. 12/785,498 and 12/824,215 addressed these concerns by providing a plurality of circuits that conditioned current from an AC input that was compatible with dimming circuits and devices and those disclosures are incorporated in full herein. While such circuits are effective at solving previous problems in the art, improvements to the circuits are still desired. Specifically, the circuits provided as shown for example only in FIG. 23 provide what is considered a dead time at zero cross. Specifically, as voltage and current go from a negative quadrant to a positive quadrant, and vice versa, or even with a waveform existing entirely in the positive quadrant, as the waveform approaches the X axis or zero cross, the current flattens at zero into and out of the zero cross by the voltage waveform. In this manner a period of zero current or dead time is presented in the circuit at the zero cross.

"This dead time is problematic when used in association with various dimmers or dimming circuits. In particular many dimmers, such as for example only, triac dimmers do not hold a charge and thus during this dead time there is no current making it difficult for the dimmer to initiate at zero cross when a reactive load is presented. Similar problems can also occur in IGBT type dimmers. As a result of difficulties in initiating in certain conditions, negative effects such as flicker and potentially perceptible flicker occurs. Thus a need in the art exists to minimize the negative effects of dead time at zero cross to improve performance of LED lighting assemblies.

"Therefore a principle objective of the present invention is to provide dimming conditioning circuitry to improve performance of current conditioning in association with a circuit receiving an AC based input."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "Apparatus and associated methods involve operation of an LED light engine in which a relative intensities of selected wavelengths shift as a function of electrical excitation. In an illustrative example, current may be selectively and automatically diverted substantially away from at least one of a number of LEDs arranged in a series circuit until the current or its associated periodic excitation voltage reaches a predetermined threshold level. The diversion current may be smoothly reduced in transition as the excitation current or voltage rises substantially above the predetermined threshold level. A color temperature of the light output may be substantially changed as a predetermined function of the excitation voltage. For example, some embodiments may substantially increase or decrease a color temperature output by a solid state light engine in response to dimming the AC voltage excitation (e.g., by phase-cutting or amplitude modulation).

"In various examples, selective current diversion within the LED string may extend the input current conduction angle and thereby substantially improve power factor and/or reduce harmonic distortion for AC LED lighting systems.

"Various embodiments may achieve one or more advantages. For example, some embodiments may substantially reduce harmonic distortion on the AC input current waveform using, for example, very simple, low cost, and low power circuitry. In some embodiments, the additional circuitry to achieve substantially reduced harmonic distortion may include a single transistor, or may further include a second transistor and a current sense element. In some examples, a current sensor may be a resistive element through which a portion of an LED current flows. In some embodiments, significant size and manufacturing cost reductions may be achieved by integrating the harmonic improvement circuitry on a die with one or more LEDs controlled by harmonic improvement circuitry. In certain examples, harmonic improvement circuitry may be integrated with corresponding controlled LEDs on a common die without increasing the number of process steps required to manufacture the LEDs alone. In various embodiments, harmonic distortion of AC input current may be substantially improved for AC-driven LED loads, for example, using either half-wave or full-wave rectification. Some implementations may require as few as two transistors and three resistors to provide a controlled bypass path to condition the input current for improved power quality in an AC LED light engine. Some implementations may provide a predetermined increase, decrease, or substantially constant color temperature over a selected range of input excitation.

"The details of various embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1 depicts a schematic representation of an example AC LED circuit with LEDs configured as a full-wave rectifier and a string of LEDs configured to receive unidirectional current from the rectifier.

"FIGS. 2-5 depict representative performance curves and waveforms of the AC LED circuit of FIG. 1.

"FIGS. 6-9 depict some exemplary embodiments of the full-wave rectifier lighting system with selective current diversion for improved power quality.

"FIGS. 10-11 depict AC LED strings configured for half-wave rectification without selective current diversion.

"FIGS. 12-13 depict an example circuit with AC LED strings configured for half-wave rectification with selective current diversion.

"FIGS. 14-16 disclose an AC LED topology using conventional (e.g., non-LED) rectifiers.

"FIGS. 17-19 disclose exemplary embodiments that illustrate selective current diversion applied to the AC LED topology of FIG. 14.

"FIG. 20 shows a block diagram of an exemplary apparatus for calibrating or testing power factor improvements in embodiments of the lighting apparatus.

"FIG. 21 shows a schematic of an exemplary circuit for an LED light engine with improved harmonic factor and/or power factor performance.

"FIG. 22 shows a graph of normalized input current as a function of excitation voltage for the light engine circuit of FIG. 21.

"FIG. 23 depicts oscilloscope measurements of voltage and current waveforms for an embodiment of the circuit of FIG. 21.

"FIG. 24 depicts power quality measurements for the voltage and current waveforms of FIG. 23.

"FIG. 25 depicts a harmonic profile for the voltage and current waveforms of FIG. 23.

"FIG. 26 shows a schematic of an exemplary circuit for an LED light engine with improved harmonic factor and/or power factor performance.

"FIG. 27 shows a graph of normalized input current as a function of excitation voltage for the light engine circuit of FIG. 26.

"FIG. 28 depicts oscilloscope measurements of voltage and current waveforms for an embodiment of the circuit of FIG. 26.

"FIG. 29 depicts power quality measurements for the voltage and current waveforms of FIG. 28.

"FIG. 30 depicts oscilloscope measurements of voltage and current waveforms for another embodiment of the circuit of FIG. 26.

"FIG. 31 depicts power quality measurements for the voltage and current waveforms of FIG. 30.

"FIG. 32 show oscilloscope measurements of voltage and current waveforms for the embodiment of the circuit of FIG. 26 as described with reference to FIGS. 27-29.

"FIG. 33 depicts power quality measurements for the voltage and current waveforms of FIG. 32.

"FIG. 34 depicts harmonic components for the waveforms of FIG. 32.

"FIG. 35 depicts a harmonic profile for the voltage and current waveforms of FIG. 32.

"FIGS. 36-37 shows a plot and data for experimental measurements of light output for a light engine as described with reference to FIG. 27.

"FIG. 38 shows a schematic of an exemplary circuit for an LED light engine that utilizes dimming conditioning circuitry.

"FIG. 39 depicts oscilloscope measurements of voltage and current waveforms for an embodiment of the circuit of FIG. 38.

"FIG. 40 shows a schematic of an exemplary circuit for an LED light engine that utilizes dimming conditioning circuitry.

"FIG. 41 depicts oscilloscope measurements of voltage and current waveforms for an embodiment of the circuit of FIG. 40.

"FIG. 42 shows a schematic of an exemplary circuit for an LED light engine that utilizes dimming conditioning circuitry.

"FIG. 43 depicts oscilloscope measurements of voltage and current waveforms for an embodiment of the circuit of FIG. 42.

"FIG. 44 shows a schematic of an exemplary circuit for an LED light engine that utilizes dimming conditioning circuitry.

"FIG. 45 depicts oscilloscope measurements of voltage and current waveforms for an embodiment of the circuit of FIG. 42.

"FIGS. 46-48 show multiple schematic diagrams of dimming conditioning circuitry.

"Like reference symbols in the various drawings indicate like elements."

For additional information on this patent application, see: Grajcar, Zdenko; Klassen, Brad; Erickson, Leif. Spectral Shift Control for Dimmable Ac Led Lighting. Filed December 30, 2013 and posted May 1, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=4652&p=94&f=G&l=50&d=PG01&S1=20140424.PD.&OS=PD/20140424&RS=PD/20140424

Keywords for this news article include: Patents, Electronics, Semiconductor.

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Source: Electronics Newsweekly


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